BAGHDAD — Suicide attackers rammed car bombs on Friday into a bus carrying Iranian pilgrims and a police checkpoint west of Baghdad, killing 16 people in all, in the latest bout of violence to rattle Iraq.

The attacks follow the deadliest two months in Iraq in half a decade, raising fears the country is descending into a renewed wave of widespread killing like the one that drove the nation to the brink of civil war following the U.S.-led invasion.

Friday’s first attack struck in the morning, when a suicide bomber drove his explosives-laden car into a bus carrying Iranian Shiite pilgrims who were on their way to visit shrines in the holy city of Najaf.

The attack took place near the town of Muqdadiyah, about 90 kilometers (60 miles) north of Baghdad. Police said eight people were killed and 25 were wounded in the blast.

Since the 2003 invasion, foreign pilgrims from Iran and other countries have poured into Najaf, whose Imam Ali shrine is one of the holiest sites for Shiite Muslims.

In the evening, attackers drove two more car bombs into a major highway checkpoint between the cities of Fallujah and Ramadi in the Sunni-dominated Anbar province west of Baghdad, detonating them nearly simultaneously.

Four police officers and four civilians died in that attack, according to police.

Medical officials confirmed the causality figures. All officials spoke on condition of anonymity because they were not authorized to talk to reporters.

Iraq has been ravaged by a spike in violence in recent weeks, with recent monthly death tolls rising to levels not seen since 2008. According to the United Nations, at least 1,045 Iraqi civilians and security personnel were killed in May. The tally surpassed April’s 712 killed.

There was no immediate claim of responsibility for Friday’s attacks, but Sunni extremists frequently target the Shiite-led government’s security forces and Shiite pilgrims, who they believe are not true Muslims.

The attacks came a day after a series of car bomb explosions in and around Baghdad killed 14 people.